Integrated multi-feedstock lignocellulosic biorefineries for sustainable biodiesel production: A techno-economic and environmental review

The depletion of fossil fuels and the increase in Greenhouse Gas emission have increased interest in sustainable alternative fuels. Lignocellulosic biomass-derived second-generation biodiesel provides many advantages over first-generation biodiesel because it utilizes non-food feedstocks such as agricultural residues, forestry waste, and industrial byproducts. This review presents a systems-level overview of integrated multi-feedstock lignocellulosic biorefineries for the sustainable production of biodiesel. Major processes such as feedstock selection, pretreatment, enzymatic hydrolysis, microbial lipid production, transesterification, and coproduct valorization are critically reviewed here. Special attention is given to oleaginous microorganisms like Rhodotorulatoruloides that can co-utilize C5/C6 sugars for increased lipid accumulation. Furthermore, lignin and hemicellulose valorization pathways are discussed as a means to enhance process economics and efficiency. Techno-economic assessment demonstrates the potential of integrated lignin-valorizing biorefineries to decrease the minimum selling price of biodiesel by 20–35% and the life-cycle greenhouse gas emissions to 10–25 g of CO 2 eq./MJ compared to fossil diesel. Emerging approaches such as AI-assisted optimization, advanced metabolic engineering, digital biorefinery integration, and deep eutectic solvent pretreatment will also be covered in future work related to commercialization. Overall, integrated biorefineries present a method to recycle agricultural waste into renewable fuels and bioproducts at a greater economic benefit.